Compact thermal card printers have been widely used for printing images or patterns on a recording medium such as an identification card, a credit card and a telephone card. In order to print such images and patterns on both sides of the card, card printers of the prior art typically include two sets of printing unit and means, causing the printers to become large in size, heavy in weight, complicated in design as well as high in cost. Since the card is the stiff material, the reversing device used in the traditional copy machines is not suitable for the card printing purpose. Hence, specially designed card-reversing (i.e., card-flipping) devices have been then used to perform printing on the both sides of the card with a printing system that is capable of printing only on one side of the card.
As one related art, the CHEETAH card printer produced by the Fargo Co. employs a clutch to turn over a card for double-side printing. Referring to FIG. 1, the roller 14 is first driven to feed the card 10 into the rotary body 12. Then, the clutch 16 is actuated to cause the rotary body 12 to be turned over by the roller 14. Although the structure of the card-reversing device is simple, the cost of the clutch 16 is expensive.
Referring to FIG. 2, the card-reversing device of the IRIS card printer produced by the NEW CODE Co. is shown. The first roller unit 17 is driven to feed the card 10 into a rotary body. The turnover motor 24 is then actuated to drive the O-ring 20 and the turnover pulley 22 to turn the card 10 over. The second roller unit 18 is used to feed the card 10 out.
In another prior art reference, a card-reversing device for a card printer is disclosed in the U.S. Pat. No. 5,771,058, which teaches the use of a device that includes four transmission means, two roller units and a rotary body. Referring to FIG. 3, the rollers 27 and 28 are used to feed the card 10 in. Driven by the belt 30, the rollers 31 and 32 can move the card 10 forward. To turn the card 10 over, the belt 34 is driven to rotate the rotary body.
In the above related art, the cost of the CHEETAH card printer is high since a clutch is used therein. The structures of the card-reversing devices in the last two related arts, i.e. the IRIS card printer and the card printer disclosed in the U.S. Pat. No. 5,771,058, are very complicated, thus increasing the difficulty of assembly and the cost of production. In addition, all card-reversing devices of the related art described above can be easily damaged, when their turnover operation is suddenly and abnormally stopped.